Electron guns with linear thermal cathode have been well known, in particular they were described in the patents for invention of Ukraine No. 21440A (B. A. Movchan, V. A. Timashov, Ye. L. Piiuk), No. 43927 (B. A. Movchan, O. Ya. Gavriliuk), No. 93182 (V. A. Timashov, O. L. Zhdanov, S. I. Ryabenko, A. A. Tsepkalov, S. Berns) and others. Their design features a beam guide, an accelerating anode and a cathode assembly that comprises a frame or cathode plate, insulators, cathode holders, and a focusing electrode. The focusing electrode is placed coaxially with the linear thermal cathode and that is why these electron guns have been named as the axial guns.
In addition, the axial electron guns are widely used in the process of electron-beam deposition of ceramic materials based on ZrO2, Gd2O3 or other oxides with heat-insulation properties on turbine blades of gas-turbine engines. Fabrication of new materials and coatings in production quantities implies the production of final products with consistent physical and mechanical properties and performance. These requirements may be only complied with if the electron gun maintains process parameters invariable during sufficient time of its service life.
At present, the stable operation of electron guns of known designs can be ensured by using the cathodes made of single-crystal tungsten with precise alignment of the crystal growth axis with respect to the cathode's working surface. This results in high costs of the gun itself as well as the products fabricated with the use of such a gun. If the cathodes made of cheaper polycrystalline tungsten are applied some problems will occur. Under effect of high temperatures the cathode changes its shape and this results in its displacement from the original position in the gun's electron-optical system and changes in focusing and positioning of the electron beam. Due to these effects the electron beam can strike the internal parts of the beam guide with their subsequent melting and flashing of the gun's accelerating anode. At that the stability of parameters and operation reliability of the axial electron gun deteriorate significantly.
Thus, the general deficiency of the well-known designs of electron guns with a linear thermal cathode of polycrystalline tungsten is a low stability of their operation due to misalignment of the electron beam due to high-temperature deformation of the cathode and consequently changes in its position with respect to the optical axis of the electron gun. Hence the aim of the disclosed invention is to improve the reliability of operation of electron guns by ensuring the stability of their parameters. The axial electron gun designed by V. A. Timashov and co-authors of U.S. Pat. No. 8,159,118 assigned to United Technologies Corporation has been selected as a prototype.